A .410, or pretty much any shotgun with any amount of choke. is only going to be throwing a pattern a few inches wide at 8ft. A 1/2 oz load of #9 shot traveling at 1200fps is going to blow a moccasin in half at 8ft. The guy missed is what happened.
I missed the 8 ft range part; if that is accurate I would also expect even #9 shot to be effective.
Might be a case of the guy looking at the end of the barrel but not quite down the barrel.